Montgomery County Executive Isiah Leggett, the son of a sawmill laborer who rose from the Jim Crow South to become a Howard University law professor and chairman of the Maryland Democratic Party, said Tuesday he will not seek a fourth term.

“I don’t want to use the word retire, but I’m not running,” said Leggett, 71, first elected to the executive’s post in 2006.

Leggett, the county’s first African American council member and county executive, has broadly signaled since his 2014 reelection that he would not run again. But with the 2018 political cycle set to begin after the Nov. 8 general election, he has started saying so explicitly in public comments. On Sunday, he told a crowd at a Silver Spring fundraiser for “No On B,” the group opposed to the term-limits ballot question, that he was done.

“It’s the first time I’ve heard him say it to an audience in public,” said council member George L. Leventhal (D-At Large), who attended the event at Denizens Brewing Co. Leventhal acknowledged that he pays close attention to Leggett’s comments on the subject — he’s one of several council incumbents looking closely at a run for county executive in 2018. He joins council members Roger Berliner (D-Potomac-Bethesda), Marc Elrich (D-At Large), Nancy Floreen (D-At Large) and Craig Rice (D-Upcounty) as possible contenders.

Most of these hopefuls were poised to run in 2014, after Leggett passed the word that his wife, Catherine, wanted him to leave after two terms. He changed his plans, creating a kind of generational logjam in county politics.

This time, he said, it’s real. “I’m not running again. Period,” Leggett said.

If Question B is approved by voters next month, Leggett would have no choice but to leave. The proposed charter amendment limits the executive and council members to three terms.

He said the term limits proposition — which he opposes — has nothing to do with his decision. Nor, he said, does his health: He has undergone two surgeries over the past year for spinal stenosis, a narrowing of the spine that can cause pain by compressing nerves in the back. He said his condition is much improved.

Leggett has presided over dramatic change on his watch, as Montgomery accelerated its transition from a cosseted, largely white suburb to a rapidly urbanizing “majority minority” jurisdiction with deepening pockets of poverty.

His own story embodies the turbulent change that overtook the county and the country. The seventh of 13 children raised in central Louisiana, he attended historically black Southern University in Baton Rouge, where he was in the middle of the burgeoning battle for civil rights. He also served four years in the Army, including an infantry stint in South Vietnam.

Montgomery was 85 percent white in the mid-1980s when Leggett, then head of the county’s Human Relations Commission, launched his first council campaign. He did not use a photograph in his early campaign literature. After four terms on the council and a stint chairing the Maryland Democratic Party, he ran for county executive in 2006.

Leggett said he regards as one of his proudest accomplishments keeping the county on a steady financial footing through recession and sequestration — a program of automatic cuts to federal government spending. He also points to significant county investments in affordable housing and capital construction projects. Later this month, the county will open its new Public Safety Training Academy in Gaithersburg, new community recreation centers in Potomac and Sandy Spring, and a new fire station in Glenmont. A “smart growth” initiative encouraging development around mass transit in White Flint and Shady Grove will also leave a lasting impact, he said.

“We’ve not gone around and bragged about this stuff, but go back and look at the record,” he said. Major unfinished business includes finalizing an agreement with a private developer to create a life sciences town center adjacent to the campus of the Food and Drug Administration in White Oak and launching the first segment of the county’s bus rapid-transit system.

Leggett’s legacy will also be defined by some setbacks. They include the Silver Spring Transit Center, which was years late and millions of dollars over budget because of design and construction problems. The county has taken contractors to court in an effort to recover extra costs.